OPEN-CHANNEL FLOWIntroduction Ch-10 of HH

Application Characteristics Section Parameters Flow State Types of Flow

Neary/S04

Application

Pressure vs. Open-channel flow

pressure flow(pressure driven)

open-channel flow(typ. gravity driven)

free-water surface

?

Section Parameters

• Reach Length =L [L]= arbitrary horizontal distance between two cross-sections

• Bed slope = So [L/L] = -dz/dx = -(z2-z1)/L = tan• Flow depth =y [L] = vertical distance from channel bottom to free

water surface• Depth of flow sec =d [L] = flow depth normal to flow, d=ycos• Top width = T[L] = Width at free-surface• Flow area = A[L2] = cross-sectional area normal to flow direction• Wetted perimeter = P[L] = length of channel boundary in contact

with water• Hydraulic radius = R[L] = A/P• Hydraulic depth = D[L] = A/T• Section Factor Critical Flow = Zc =AD1/2 [L5/2]• Section Factor Uniform Flow = Zn = AR2/3 [L8/3]

Parameters: Circular Section

do y

Flow State

Reynolds Number– Laminar flow– Turbulent flow

Froude Number– Subcritical flow– Supercritical flow– Critical flow

VR

Re

gD

VFr

Types of Flow

Variation in Time?– Steady flow velocity and depth change with time– Unsteady flow velocity and depth change with time

Variation in Space?– Uniform flow velocity and depth same at every

cross-section– Nonuniform flow velocity and depth vary between

cross-sections